Method of forming a plastic spray coated floating roof



Nov. 24, 1964 EEEEEEEEEE LS Nov. 24, 1964 E. E. MlcHAELs METHOD OF FORMING A PLASTIC SPRAY COATED FLOATING ROOF 2 lSheets-Sheet 2 Filed May l0, 1951 9716.5 mel/ United States Patent O 3,158,667 METFEGD F FQRMING A PLASTIC SFRA? COATED FLATNG R601? Ernest E. Michaels, Chicago, Iii., assigner to Chicago Bridge de Iron Company, Chicago, iii., a corporation of Iliinois Filed May 1G, 1961, Ser. No. 109,172 6 Claims. (Ul. 264-45) This invention relates to forming an improved floating roof for a vessel such as a tank used to store volatile liquids such as crude oils, gasolines, and other hydrocarbons.

Large storage tanks have been built in the field to store petroleum products, liquid chemicals and other products. Many such tanks have been equipped with steel bottoms and steel side walls of generally circular plan and have been otherwise upwardly open or have been provided v/ith roofs, depending upon their service. In order to protect the stored product from the elements, reduce fire hazards and corrosion, many of these tanks have been equipped with roofs which float' on the liquid product. It sometimes becomes necessary to install a floating roof inside an aready existing fixed roof type tank. Construction of conventional metal floating roofs inside such a roofed tank is very difiicult for obvious reasons.

It is generally accepted that to be effective, a floating roof must at all times be in contact with the stored liquid. if vapor space exists anywhere above the liquid, either excessive evaporation losses may occur or a substantial mixture of volatile gases will form and a fire or explosion may ensue.

Steel lioating roofs are well known in the art. While there have been several attempts to construct floating roofs of synthetic plastic materials within existing fixed roof tanks, these have been relatively unsuccessful. For small tanks, reasonable success can be obtained by the use of segments of foarned plastic small enough to be inserted through a manhole which are then spliced together inside the tank to form a floating cover. On tanks having large diameters, however, this scheme becomes practically impossible because of the tremendous materials handling problems involved.

The instant invention forms a plastic iioating roof which is constructed in place in a manner which minimizes the materials handling problem. The roof can quickly and easily be installed by a minimum number of workmen, both in an open tank and in a fixed roof tank. Further, the roof does not require an expensive sealing ring to adjust for possible out-of-roundness of the tank shell. Another advantage stems from the fact that plastics are generally poor conductors of electricity and therefore do not create static electricity problems which may lead to fire or explosion.

The invention will be better understood from the following detailed description thereof, taken in conjunction with the accompanying drawings, in which:

FIGURE l is a cross-sectional view of a plastic foam blanket with additional reinforcing material in the interior of the foam;

FIGURE 2 is a cross-sectional View of the foam blanket of FIGURE l without the additional reinforcing material;

FIGURE 3 is a cross-sectional view of a fiberglass reinforced plastic blanket with no external impervious films;

FIGURE 4 is a cross-sectional view of one of the variety of rim seals which may be employed on the plastic floating roof;

FIGURE 5 is a sectional elevation view of an open top tank showing a sprayed plastic floating roof resting on the bottom of the tank;

FIGURE 6 is a sectional elevation view of an open top tank with the plastic roof iioating on the surface of the stored liquid; and

race

FIGURE 7 is a sectional elevation view of a fixed roof tank with the iioating roof installed.

In the drawings, FIGURE l shows a sprayed plastic foam blanket 2 underlined with a thin paper, cloth, or plastic film 1 and containing a suitable embedded reinforcing material 3. In accordance with the invention, a oating roof is comprised of such a plastic blanket.

FIGURE 2 shows another embodiment of sprayed plastic foam blanket 2 and the underlying thin paper, cloth, or plastic film ll. Generally, the construction shown in FIGURE 2 is used in tanks of smaller diameter or where there is less atmospheric turbulence than the construction shown in FIGURE 1. Generally, it is desirable to use the thin layer of paper, cloth or plastic film 1. With certain permeable porous plastic materials such as open cell polyurethane of either the ester or ether types, the film 1 must be provided on both the upper and lower surfaces of the plastic foam blanket in order to prevent evaporation of the stored product. The preferred plastic foam material 2 is closed cell urethane. This type of plastic, after spraying, hardens in a non-resilient, small pored, rather rigid mass. With this type of foam blanket, it is not necessary that lower film 1 be used (FIGURE 3), but it' is generally desirable to provide such a film as an added safety factor with regard to evaporation, as additional reinforcement to prevent cracking of the foam blanket, and to prevent adhesion to the tank bottom during the spraying operation. The preferred material for the film 1 is a plastic of the polyester variety; but, because they are not generally subject to atmospheric deterioration, a suitable plasticized paper, or a cloth of synthetic plastic fibers, can also be used.

The reinforcement 3 embedded in the foam plastic Z as shown in FIGURE 1 is preferably used in all roofs of large diameter as well as in those which are directly exposed to the element's of wind and rain, in order to prevent destruction of the roof or impairment of its efficiency. Many materials may be used for this reinforcement, including an open weave synthetic fiber cloth, glass fibers, rough finish plastic film or a screen of the chicken wire type constructed of fine metal wire. Chicken wire provides a very strong reinforcement with minimum weight.

FIGURE 5 shows an open top metal tank 1d consisting of a cylindrical side wall 11 and a fiat bottom 12. The tank of FIGURE 5 is of considerably simplified construction to show the method of constructing the floating roof of the invention without the obstructive piping generally found in these tanks, such as that shown in FIGURE 7. In the tank of FIGURE 5, a thin plastic film corresponding to film 1 of FIGURE 1, or other release agent such as a film of oil or grease, is first placed on the tank bottom 12. In the case of a plastic film, it is preferably attached to a rim seal 13 by any suitable means. Rim seal 13 is suitably constructed of a stiff plastic, rubber or plasticized cardboard and is provided so that the floating roof will not bind on the tank shell 11 as it moves up and down with the surface of the stored product. Any suitable means may be used to prevent the roof from binding and to minimize evaporation, such as a toroidally shaped tube extending around the inside of the tank and attached directly to the thin film. Alternatively, if an open cell foam polyether is used as the material for lthe fioating roof 14, it can easily be looped at the edge to form a seal which will slide up and down without binding on the tank wall and will still minimize evaporation loss. One such rim seal is shown in FIGURE 4, consisting of a relatively thin slab of a fiexible foam material folded over to` form an annular tube 41 and preferably covered by a vsuitable Wearresistant impermeable fabric or film material 42. The seal is held in position by means of bolts 43 which are embedded inthe foamed plastic 44 of the roof. The Shanks stesse? of the bolts are provided with lugs 46 which firmly anchor the bolt in the plastic material.

With the tilm (e.g., l. in FIGURE l) in place on the tank bottom, a polymerizable plastic blanket is sprayed over the film and the rim seal (e.g., 13 in FIGURE 5). The depth ofthe sprayed plastic 14 varies according to the variety of plastic used and the size and use of the roof. When Va urethane foam is used, a depth of 1 2 inches is generally adequate, but with polyester resins, much thinner blankets may 4be used. In a preferred embodiment using glass fiber reinforcement, the foam blanket need be only 1A to 3/s inch thick in most cases. For each diameter of roof, however, the exact thickness must be chosen to insure structural adequacy.

FIGURE 6 shows a typical embodiment of the iloating roof of the invention. The open-top metal tank 16 cornprises cylindrical sides 17 and a at bottom 18, the bottom containing a sump 19 from which water which accumulates at the bottom of the tank is drawn ofi through pipe 2l. Because of pipe 2l, the il-oating roof 22 can never rest on the tank botom 1S, so that a wire or cable support system 23 is provided, The cable or wire system 23 is dcsigned to withstand the weight of the floating roof 22 and any water load carried 'by the roof, and is made up ot a number of metal wires o-r ropes, spaced apart from and at right angles to each other, so as to form a checkerboard pattern on which the roof 22 is constructed and rests when the product is below the height of the cable system. Many suitable support systems can be devised by those skilled in the art, so ythat no undue limitations should be implied by the above description. Embedded in the foam blanket or roor" 22 are at least two plates (not shown) which are fitted with a hole through which cables or Wires 24 may be inserted to prevent excessive rotational movement of the root. The cables or wires 24 are hung vertically from the rim of Wall 17 to provide guides along which the root moves up and down with the level of the product. Wires 24 are attached to the bottom of the tank 13 at points which are projected suiiiciently inwardly to clear the sealing means 13. With the polyester resin type of roof, or the cl sed cell urethane foam roof, suitable guide means other than wires may be used because 4the roof itself is rigid enough to support the same. Light-weight metal or plastic manholes or other small holes for sampling, provided with covers, (not shown) may be placed in the floating roof 22 if desired.

At the center of roof 22 (FIGURE 6) is a drainage sump 26. Attached thereto is a ilexible pipe or tube 27 through which the drainage water passes to the outside of the tank 16. The weight of the sump 26 must be adequate to cause the roof to slant downwardly toward the center in order that rain water will drain properly. Such a slant is not needed in a floating roof built within a xed roof tank since the disposal of rain water is not a problem.

In constructing a lioating roof of the type shown in FIG- URE 6, there is rst constructed the cable support system 23. Over this system is then draped the thin iilm on which the plastic will be sprayed. Prior to spraying the plastic, it is preferred to lill the tank with liquid to the same height as the wire or cable support system 23. The liquid provides suicient support for the thin tilm and foam blanket so that no sagging will occur in the areas between the Wires of the cable support system. It is always desir-able to float the new roof on the liquid surface during the time in which the foam blanket 22 sets up and becomes rigid. This procedure yields a iiat roof which is desirable to prevent the formation of pockets which collect rain water.

FIGURE 7 shows `an embodiment of the invention within a fixed roof met-al tank 31 comprising cylindrical sides 32, roof 33, flat .bottom 34 and columns, e.g., 36, extending between the roof 33 and bottom 34 for supporting roof 33. In this embodiment there is no interior piping, so that no wire or cable support system is shown, although it would usually be required. The construction of this ernbodiment is otherwise essentially the same as that shown in the open top tank of FIGURE 6, except that ythe sealing sleeves 37 encircling each column must be provided and placed prior to spraying the plastic material. The column lsleeves 37 serve the same essential functions of minimizing evaporation loss and preventing binding of the roof on the columns as does rim seal 13.

Any plastic which is capable of resisting the deleterious etfects of weathering and chemical decomposition from the stored product can be used to form the roof of the invention. Isophthalic polyesters, epoxies and polyurethanes are examples of the variety of plastics which can be applied and polymerized in place so as to form the floating roof. Likewise, any suitable spray equipment can be employed to position plastic material in the form of the foam blanket.

While the roof of the invention is intended primarily for use infabricated storage tanks, particularly those having circular cross-sections, it should be understood that it is not restricted thereto. Tanks of any other shape, e.g`., square, rectangular, polygonal, or irregular, can also be provided with lloating roofs in accordance with the invention. Similarly, the storage vessel need not be a conventional tank at all, since any chamber capable of storing volatile liquids, eg., an underground cavern, either natural or man-made, or a suitable excavation at ground level, could also be used in the invention.

The foregoing detailed description is given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, as modilications will be obvious to those skilled in the art.

What is claimed is:

l. The method of forming a floating roof in place within a vessel for the storage of v-olatile liquids cornprising the steps of securing a sheet of a thin material in a substantially horizontal position covering substantially the entire cross-sectional area of said vessel, securing an upstanding rim seal to the edge of said sheet adjacent the wall of said vessel to form a buoyant structure, coating said sheet and said rim seal with a layer of a polymerizable plastic material which in its polymerized form is relatively light and unaffected by contact with said volatile liquids, and polymerizing said plastic material.

2. The method of claim 1 in which said plastic material is a plastic foam.

3. The method of claim l in which said sheet is supported by the bottom of said vessel during the application of said plastic material.

4. The method of claim l in which said sheet is supported by 4a grid above the bottom of said vessel during the application of said plastic material.

5. The method of claim l in which said plastic material is applied to said sheet by spraying.

6. The method of claim l in which said plastic material contains a reinforcing material.

References Cited in the tile of this patent UNITED STATES PATENTS 1,887,847 Peiper Nov. 15, 1932 2,567,920 Allen Sept. 18, 1951 2,824,036 Dykemalm et al. Feb. 18, 1958 2,873,042 Fino Feb. 10, 1959 2,907,627 Cummings Oct. 6, 1959 2,919,047 Fino Dec. 29, 1959 2,976,577 Gould Mar. 2S, 19,61 3,001,542 Shepherd et al Sept. 26, 1961 3,036,342 Fino hrlay 29, 1962 3,082,486 Khawam et d Mar. 26, 1963 FOREIGN PATENTS 221,672 Australia NOV. 21, 1957 815,105 Great Britain June 17, 1959 OTHER REFERENCES Science News Letter, Sun-Proof Igloo, January 2, 1960, pageV 7. 

1. THE METHOD OF FORMING A FLOATING ROOF IN PLACE WITHIN A VESSEL FOR THE STORAGE OF VOLATILE LIQUIDS COMPRISING THE STEPS OF SECURING A SHEET OF A THIN MATERIAL IN A SUBSTANTIALLY HORIZONTAL POSITION COVERING SUBSTANTIALLY THE ENTIRE CROSS-SECTIONAL AREA OF SAID VESSEL, SECURING AN UPSTANDING RIM SEAL TO THE EDGE OF SAIDSHEET ADJACENT THE WALL OF SAID VESSEL TO FORM A BUYANT STURCTURE, COATING SAID SHEET AND SAID RIM SEAL WITH A LAYER OF A POLYMERIZABLE PLASTIC MATERIAL WHICH IN ITS POLYMERIZED FORM IS RELATIVELY LIGHT AND UNAFFECTED BY CONTACT WITH SAID VOLATILE LIQUIDS, AND POLYMERIZING SAID PLASTIC MATERIAL. 